The present invention relates to a process for classifying a crystal mixture or for concentrating rocks or mixed crystals in particle form by capturing the particles in a gas flow for separation of particles of different sizes and/or weights by means of natural or artificial gravity. The present invention is particularly suitable for classifying a mixture of different kinds of crystal particles or for concentrating finely divided rocks or mixed crystals with densities so close to each other that they cannot in any practical way be separated using conventional methods or means, such as flotation cells.
In this connection, `crystal mixture` is understood to mean a mixture of two or more crystal types, while the expression `mixed crystals` refers to a mixture of crystals of varying composition. An example of `artificial gravity` is represented by cyclone separation.
Nowadays, concentrating of minerals is most often accomplished by chemical flotation methods, magnetic separation methods or by grinding or sifting methods. According to their chemical, physical or structural properties, minerals behave in different ways depending on the environment in which they are treated. Different minerals require different concentrating methods, which naturally also have their peculiar advantages and disadvantages. Chemical flotation methods require chemicals which, in view of environment protection, should be maximally recoverable and reusable. The flotation processes of prior art are to a large extent based on practical applications, which implies that it is difficult to predict the course of the process directly on the basis of chemical and physical laws. Concentration by grinding and sifting is greatly dependent on the different minerals' physical properties, the hardness of the minerals being decisive, and grinding equipment of a special nature is frequently needed in order to attain good concentration results.
The object of the present invention is therefore to provide a process for classifying a crystal mixture or for concentrating rocks or mixed crystals in particle form wherein the different particles have so closely identical properties under normal separation circumstances that separation is either impossible or hard to accomplish, or to induce a selective change in those properties on which the separation is based, so that the separation is substantially facilitated.